I took my dogs to a boarder about 3 months ago, so I could go on vacation. When I got them back, it was constant itching and sores all over them. I thought it was mange and took 2 of the 6 to the vet. He did scrapings and told me it was not mange, but flea allergies. I had to treat all the dogs with antibiotics, benadryl and shampoo them with a good flea shampoo. This worked for awhile and then it started over again. I had had a swimming pool in my back yard and sold it. The foundation of that pool was sand, giving rise to many sand fleas and reinfecting my dogs. So besides bombing my house and putting frontline on the dogs, I had to treat my yard with a flea and tick killer. This seems to be helping and my dogs are more comfortable, but it is an ongoing process and all steps must be taken or the allergies come right back. I love my dogs, so it's worth it. Hope this info helps someone else.

I have a cat who is allergic to fleas! (Kinda cruel joke of Nature, doncha think?)

I've used Frontline and Top Spot, but in the last year have been using Revolution. I like it better.
It is for many things besides fleas:
In dogs, it controls heartworms, ear mites and sarcoptic mange.

http://www.petalia.com.au/templates/prodSubList.cfm?group_no=2002&specie=Home_ca

You might want to see what your vet says.